1. Field of the Invention
The present invention relates to an image reading apparatus, and particularly to an image reading apparatus which allows reading of an image recorded on a photographic film by separating the image into a plurality of component colors.
2. Description of the Related Art
There has recently been proposed a photographic processing method in which a film image recorded on a photographic film is read in such a manner as to be separated into component colors of R, G, and B, and image data obtained by reading the film image is subjected to image processing such as various corrections, and thereafter, an image is recorded on a recording material or is shown on a display. This photographic processing method has an advantage over conventional photographic processing methods in which a film image is recorded on a photographic printing paper by surface exposure in that the quality of a recorded image can be freely controlled by image processing for image data. However, the quality of the recorded image also depends on the quality of image data prior to image processing, i.e., the reading accuracy of a film image, and therefore, an image reading apparatus which allows reading of the film image with high accuracy and at high speed, namely, at a speed equal to or higher than the processing speed in the conventional photographic processing method becomes necessary.
There have conventionally been proposed various image reading apparatus structures which, as described above, read an image recorded on an original such as a photographic film so that the image is separated into a plurality of component colors, and outputs image data for the purpose of recording the image on the recording material, and the like. For example, there is known a process color scanner in which, with an original being wound onto an outer periphery of a cylindrical drum along the circumferential direction of the drum, the drum and the original are rotated integrally so as to allow relative movement of the original and a reading head disposed on the outer peripheral side of the drum, and white light emitted from a light source disposed within the drum and irradiated on and transmitted through the original is separated into a plurality of component colors and read by the reading head, and thereby obtaining image data of an image recorded on the original (see Japanese Patent Application Laid-Open (JP-A) No. 58-9145).
However, in the above-described color scanner, the circumferential length of the drum must be longer than the length of the recording material. When the color scanner is used for reading a film image recorded on an elongated photographic film, the diameter of the drum must be increased greatly due to the length of elongated photographic film such as 36 exposure size 135 film. Unfortunately, the apparatus must be made much larger. Further, during reading of the film image, a complicated operation is required in which a photographic film to be read is wound onto the drum and is set to be positioned at a fixed location on the outer peripheral surface of the drum. For this reason, operators have to carry out a great deal of labor and it is difficult to read a large amount of film images at high speed. Moreover, the above-described color scanner provides, as a precondition, reading of a positive image recorded on an original. For this reason, although there is no light controlling filter or the like for setting, at an arbitrary value, the ratio of the amount of light between component colors of light irradiated from the light source to the original, it is desirable that, in order to allow accurate reading of a negative image, a light controlling filter or the like be provided. With the above-described structure, however, provision of the light controlling filter or the like is difficult.
Further, in the industrial field of printing, the level of image quality required is very high. In order to acquire image data used for printing, the image must be read with extremely high accuracy. Accordingly, among image reading apparatuses for printing, there may be found a structure in which the flatness of an original is improved by setting the original in a cassette so that the entire surface of the original is held by a transparent flat plate. Then, a reading sensor and the original are moved relative to each other while the cassette in which the original is set is conveyed at a constant speed to allow reading of an image recorded on the original.
However, even when the above structure is applied to the reading of a film image, in the same manner as in the above-described color scanner, there is required a complicated operation in which a photographic film to be read is set in a cassette when reading the film image. For this reason, operators have to carry out a great deal of labor and it is difficult to read large amounts of film images at high speed. Further, when the cassette is formed so that an elongated photographic film is held over the entire surface thereof, the cassette becomes extremely large. Accordingly, it is not practical that the above-described technique be applied to effect reading of a film image recorded on the elongated photographic film.
Further, as an image reading apparatus for reading a film image, there is known a structure in which, with an area CCD sensor, which has a two-dimensional arrangement of a large number of photoelectric conversion elements and CCD cells, being used as a reading sensor, an elongated photographic film is intermittently conveyed so that film images recorded on the photographic film are each positioned sequentially at an image reading position set by the area CCD sensor, and these film images are sequentially read by the area CCD sensor (for example, FUJI FILM DEGITAL LAB SYSTEM, FRONTIER, (SCANNER & IMAGE PROCESSOR) SP-1000).
However, since the area CCD sensor is provided with a large number of photoelectric conversion elements and CCD cells, it is generally expensive. In order to read an image at a higher resolution, it is necessary to use an area CCD sensor having an extremely large number of cells proportional to the square of resolution, and therefore, there is a drawback in that the cost increases. Further, there is a possibility that area CCD sensors coming into the market as products may include a small number of cells from which a signal properly corresponding to the amount of incident light is not outputted due to the yield rate at the time of manufacturing (the so-called defective pixels), and therefore, a problem also exists in that a complex correction circuit becomes necessary so as to correct the defective pixels.
Moreover, there is also known an image reading apparatus of a simple structure which allows reading of a film image. In this device, a fluorescent lamp is used as the light source, and a light controlling filter for controlling the ratio in the amount of light between component colors of light irradiated on the photographic film, and a light diffusion box which diffuses light to be irradiated on the photographic film so as to alleviate nonuniformity of the amount of light are not provided. As a result, light from the light source is directly irradiated on the photographic film. This image reading apparatus is used to simply read a film image and does not allow highly accurate reading of a film image.
In addition, Japanese Patent Application Laid-Open (JP-A) Nos. 6-242521 and 6-242522 each disclose an image reading apparatus structured in such a manner that a pre-scan section in which a film image is preliminarily and roughly read by a line CCD and a fine-scan section in which a film image is read by the line CCD at a high resolution are disposed parallel to each other along a direction in which an elongated photographic film is conveyed, and a gradation conversion condition is prepared based on pre-scan image data obtained by reading the film image in the pre-scan section, and further, gradation conversion is effected for fine-scan image data obtained by reading the film image in the fine-scan section in accordance with the gradation conversion condition.
However, in the above-described structure, it is necessary that two sets of optical components including a line CCD, a light source, and an imaging lens be provided, and therefore, there arise problems in that the cost therefor increases and the structure becomes complicated. Further, in the above-described image reading apparatus, in consideration of a resolution for image reading required for the fine-scan section, a time required for a process effected based on the pre-scan image data, and the like, the resolution for image reading in the fine-scan section needs to be about ten times that for image reading in the pre-scan section. For this reason, it is necessary that the conveying speed of the photographic film in the pre-scan section and the conveying speed of the photographic film in the fine-scan section widely differ from each other and that a film buffer be provided between the pre-scan section and the fine-scan section so as to eliminate the difference in the conveying speed of the photographic film. The film buffer also causes complication of the structure.
Further, the position where the film image is recorded on the photographic film is not fixed. Accordingly, in the above-described structure, reading of the film image is effected in such a manner that a position where the film image is recorded is sequentially determined by an image plane detecting sensor while conveying the photographic film, and determination of the image recorded position and reading of the film image are effected concurrently. For this reason, it is necessary that the conveying speed of the photographic film be made relatively low. As a result, there also arises a problem in that the film image cannot be read at high speed.